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(#) Using Private APIs

!!! WARNING: Using Private APIs
   This is a warning.

Id
:   `PrivateApi`
Summary
:   Using Private APIs
Severity
:   Warning
Category
:   Correctness
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   3.0.0 (October 2017)
Affects
:   Kotlin and Java files
Editing
:   This check runs on the fly in the IDE editor
See
:   https://developer.android.com/preview/restrictions-non-sdk-interfaces
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/PrivateApiDetector.kt)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/PrivateApiDetectorTest.kt)

Using reflection to access hidden/private Android APIs is not safe; it
will often not work on devices from other vendors, and it may suddenly
stop working (if the API is removed) or crash spectacularly (if the API
behavior changes, since there are no guarantees for compatibility).

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
src/test/pkg/myapplication/ReflectionTest1.java:8:Warning: Accessing
internal APIs via reflection is not supported and may not work on all
devices or in the future [PrivateApi]
    Class&lt;?&gt; c = Class.forName("com.android.internal.widget.LockPatternUtils"); // ERROR
                 -------------------------------------------------------------
src/test/pkg/myapplication/ReflectionTest1.java:9:Warning: Accessing
internal APIs via reflection is not supported and may not work on all
devices or in the future [PrivateApi]
    int titleContainerId = (Integer) Class.forName("com.android.internal.R{$}id").getField("title_container").get(null);
                                     --------------------------------------------
src/test/pkg/myapplication/ReflectionTest1.java:11:Warning: Accessing
internal APIs via reflection is not supported and may not work on all
devices or in the future [PrivateApi]
    Class SystemProperties = cl.loadClass("android.os.SystemProperties");
                             -------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here is the source file referenced above:

`src/test/pkg/myapplication/ReflectionTest1.java`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers
package test.pkg.myapplication;

import android.app.Activity;

public class ReflectionTest1 extends Activity {
    public void testForName(ClassLoader cl) throws Exception {
        Class.forName("java.lang.String"); // OK
        Class<?> c = Class.forName("com.android.internal.widget.LockPatternUtils"); // ERROR
        int titleContainerId = (Integer) Class.forName("com.android.internal.R{$}id").getField("title_container").get(null);
        @SuppressWarnings("rawtypes")
        Class SystemProperties = cl.loadClass("android.os.SystemProperties");
    }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/PrivateApiDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `PrivateApiDetector.testForNameOnInternalClass`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=192708.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a suppression annotation like this on the enclosing
  element:

  ```kt
  // Kotlin
  @Suppress("PrivateApi")
  fun method() {
     forName(...)
  }
  ```

  or

  ```java
  // Java
  @SuppressWarnings("PrivateApi")
  void method() {
     forName(...);
  }
  ```

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection PrivateApi
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="PrivateApi" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'PrivateApi'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore PrivateApi ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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